A large new study has examined the effects of vitamin D on a diverse group of adults and found no evidence that this supplement can prevent type 2 diabetes.

vitamin D shape made of pills on blue backgroundShare on Pinterest
Vitamin D supplements don’t do much to prevent type 2 diabetes.

Vitamin D is an essential vitamin; it builds and maintains healthy bones.

Our bodies produce vitamin D in response to sun exposure, and they can only absorb alcium, the main component of bones, when this vitamin is present.

We can also find vitamin D in certain foods, such as salmon, mackerel, sardines, and fortified milk and cereals. Supplements are also available.

In addition to ensuring the health of bones and teeth, vitamin D can offer other health benefits.

Vitamin D supports the brain and immune and nervous systems. It also helps regulate insulin levels, promotes cardiovascular health, and may help prevent cancer. Official guidelines recommend that adults take 600 International Units (IU), or 15 micrograms (mcg), of vitamin D daily.

It is important to keep in mind that high doses of vitamin D may have side effects. A 2010 study, for example, showed that too much vitamin D among older women may lead to falls and bone fractures. It may also raise the risk of kidney stones among women.

Now, a large-scale study called D2d — which the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) funded — has examined whether or not vitamin D supplementation can prevent type 2 diabetes. The study also shed light on the benefits and side effects of this vitamin.

A diverse group of more than 2,000 adults from 22 sites across the United States participated in the study. The results now appear in the New England Journal of Medicine, and the scientists presented them at the American Diabetes Association annual meeting in San Francisco, CA.

“Observational studies have reported an association between low levels of vitamin D and increased risk for type 2 diabetes […]. However, whether vitamin D supplementation may help prevent or delay type 2 diabetes was not known,” explains Dr. Myrlene Staten, a D2d project scientist at the NIDDK.

The researchers measured the participants’ vitamin D levels at the beginning of the study and found that around 80% of them had sufficient levels of vitamin D based on the recommended intake. Then, the scientists divided them into groups that took either 4,000 IU of vitamin D or a placebo pill daily.

The scientists screened the participants every 3–6 months for an average of about 2 years. At the end of the analysis, they found that 293 out of 1,211 participants in the vitamin D group developed diabetes. Meanwhile, 323 out of 1,212 in the placebo group developed it.

The difference between the two groups was not statistically significant.

D2d is the largest study to date to examine whether daily vitamin D can help prevent type 2 diabetes. In addition to its size, it also included a diverse group of adults in terms of race, sex, age, and body mass index (BMI). The size and diversity of the cohort ensure that the results are applicable on a large scale.

“When the study ended, we found no meaningful difference between the two groups regardless of age, sex, race, or ethnicity,” reports lead study author Dr. Anastassios G. Pittas, of the Tufts Medical Center in Boston, MA.

The use of dietary supplements has been increasing in the U.S., and vitamin D is one of the most common supplements among adults. In light of these trends, the D2d study also evaluated the safety of taking 4,000 IU of vitamin D daily. This is higher than the recommended dose.

Although previous studies had revealed side effects and warned against high doses of vitamin D, the results of the D2d study showed no difference in the risk of high blood calcium levels and kidney stones between the vitamin D and placebo groups.

“While we continue to search for new ways to prevent the disease, we know that lifestyle change or the drug metformin remain effective methods to prevent type 2 diabetes,” concludes Dr. Griffin P. Rodgers, director of the NIDDK.

We encourage the 84 million U.S. adults at high risk for developing type 2 diabetes to explore options like the CDC’s National [Diabetes Prevention Program], available to communities throughout the country.”

Dr. Griffin P. Rodgers